President Barack Obama sounded outrage over the shooting down of a Malaysian Airlines jet, but isn't ready to pin the blame definitively on Russian-backed separatists or Russian President Vladimir Putin.

With hawks in Congress urging a tough response against Putin after the jet was shot down over separatist-controlled territory Thursday, Obama has reacted cautiously, saying he doesn't want to get ahead of the facts.

But he said the United States believes the plane was shot down by a sophisticated surface-to-air missile from separatist-controlled territory, and noted those separatists have claimed credit for downing other aircraft.

"Over the last several weeks, Russian-backed separatists have shot down a Ukrainian transport plane and a Ukrainian helicopter, and they claimed responsibility for shooting down a Ukrainian fighter jet," Obama said. He called the act an "outrage" and "a wake-up call for Europe and the world that there are consequences to an escalating conflict in eastern Ukraine, that it is not going to be localized, it is not going to be contained. You know, what we've seen here is just in one country alone, our great allies, the Dutch, 150 or more of their citizens being killed."

Obama said there must be an investigation, and said the FBI and the National Transportation Safety Board are sending people to help investigate.

At least one U.S. citizen, he said, was among the nearly 300 on board.

"Men, women, children, infants who had nothing to do with the crisis in Ukraine," Obama said. "Their deaths are a outrage of unspeakable proportions."

Obama separately pressured Putin to rein in the rebels.

"Now I think is a somber and appropriate time for all of us to step back and take a hard look at what has happened. Violence and conflict inevitably lead to unforeseen consequences. Russia, the separatists, and Ukraine all have the capacity to put an end to the fighting," he said.

Obama also spoke briefly on Israel's ground invasion of Gaza.

"I reaffirmed my strong support for Israel's right to defend itself. No nation should accept rockets being fired into its borders or terrorists tunneling into its territory. In fact, while I was having the conversation with Prime Minister Netanyahu, sirens went off in Tel Aviv," Obama said.

"We are hopeful that Israel will continue to approach this process in a way that minimizes civilian casualties and that all of us are working hard to return to the ceasefire that was reached in November of 2012," he said.